U.S. patent application number 11/456142 was filed with the patent office on 2007-07-12 for light guide plate, and backlight module and liquid crystal display comprising the same.
This patent application is currently assigned to AU OPTRONICS CORP.. Invention is credited to Chih-Kuang Chen, Jyh-Haur Huang, Ko-Chia Kao, Jing-Huan Liao.
Application Number | 20070159852 11/456142 |
Document ID | / |
Family ID | 38232579 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070159852 |
Kind Code |
A1 |
Kao; Ko-Chia ; et
al. |
July 12, 2007 |
Light Guide Plate, and Backlight Module and Liquid Crystal Display
Comprising the Same
Abstract
A light guide plate structure, for use with a back light module
of a liquid crystal display, has a top surface, a bottom surface, a
first end portion, a second end portion which is opposite the first
end portion, and a plurality of substantially paralleled V-shape
grooves formed on the bottom surface and extending from the first
end portion to the second end portion. Each of said V-shape grooves
comprises a top angle with a continuous variation from the first
end portion to the second end portion. The present invention gets
rid of the dark areas of an LCD that appear adjacent to one of the
end portions in conventional models, thus enhancing the uniformity
in its brightness levels.
Inventors: |
Kao; Ko-Chia; (Pingtung
County, TW) ; Liao; Jing-Huan; (Taoyuan City, TW)
; Chen; Chih-Kuang; (Kaohsiung City, TW) ; Huang;
Jyh-Haur; (Pingtung County, TW) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, LLP
100 GALLERIA PARKWAY, NW, STE 1750
ATLANTA
GA
30339-5948
US
|
Assignee: |
AU OPTRONICS CORP.
Hsinchu
TW
|
Family ID: |
38232579 |
Appl. No.: |
11/456142 |
Filed: |
July 7, 2006 |
Current U.S.
Class: |
362/615 |
Current CPC
Class: |
G02B 6/0038
20130101 |
Class at
Publication: |
362/615 |
International
Class: |
F21V 7/04 20060101
F21V007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2006 |
TW |
095100937 |
Claims
1. A light guide plate having: a top surface; a bottom surface; a
first end portion; and a second end portion opposite to the first
end portion; wherein the bottom surface is formed with a plurality
of substantially paralleled V-shape grooves which extend from the
first end portion to the second end portion, and each of the
V-shape grooves has a top angle gradually varying from the first
end portion to the second end portion.
2. The light guide plate as claimed in claim 1, having a profile
gradually tapered from the first end portion to the second end
portion.
3. The light guide plate as claimed in claim 1, wherein the top
angle is gradually greater from the first end portion to the second
end portion.
4. The light guide plate as claimed in claim 1, wherein the top
angle is about 110 degrees at the first end portion and about 140
degrees at the second end portion.
5. A backlight module comprising: a light guide plate, having: a
top surface; a bottom surface; a first end portion; and a second
end portion disposed opposite to the first end portion; wherein the
bottom surface is formed with a plurality of substantially
paralleled V-shape grooves, which extend from the first end portion
to the second end portion, and each of the V-shape grooves has a
top angle gradually varying from the first end portion to the
second end portion; and an illumination device disposed on a side
of the light guide plate to provide light from the first end
portion to the second end portion.
6. The backlight module as claimed in claim 5, wherein the light
guide plate has a profile gradually tapered from the first end
portion to the second end portion.
7. The backlight module as claimed in claim 6, wherein the top
angle is gradually greater from the first end portion to the second
end portion.
8. The backlight module as claimed in claim 5, wherein the top
angle is gradually greater from the first end portion to the second
end portion.
9. The backlight module as claimed in claim 5, wherein the top
angle is about 110 degrees at the first end portion and 140 degrees
at the second end portion.
10. A liquid crystal display comprising the backlight module as
claimed in claim 5 and a liquid crystal panel disposed above the
backlight module.
11. The liquid crystal display as claimed in claim 10, wherein the
liquid crystal panel has a dimension between about 15 inches and
about 19 inches.
Description
[0001] This application claims the benefit of Taiwan Application
Serial No. 095100937, filed Jan. 10, 2006, the subject matter of
which is incorporated herein by reference.
CROSS-REFERENCES TO RELATED APPLICATIONS
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a light guide plate; more
particularly, to a light guide plate for use with an edge type back
light module of a liquid crystal display (LCD), and an LCD
comprising the light guide plate.
[0005] 2. Descriptions of the Related Art
[0006] Liquid crystal displays (LCDs) are mainstream products on
the display market. Not only does it save power and emit low
radiation, it is also lightweight and portable. It is widely used
on appliances such as televisions, general monitors, laptops,
global position systems (GPS), and mobile communicating devices.
That being said, conventional monitors are gradually being replaced
by LCDs.
[0007] The backlight module is one of the key components for
providing uniform and sufficient lights for an LCD panel. A
conductive type backlight module primarily comprises a lamp, lens
sheet (or prism sheet), light guide plate, diffusion sheet, reflect
sheet, protective film, and optical film.
[0008] Backlight modules are divided into two categories, namely,
direct types and edge types. An illumination device for use with
the edge type backlight module is disposed on the outer edge of the
light guide plate. A reflector is disposed under the light guide
plate for gathering and reflecting lights through the panel. In
comparison, the edge type backlight module has the benefit of being
slimmer than the direct type. Moreover, the edge type also has
fewer heat problems.
[0009] A backlight module demands uniform and high brightness
levels, low cost, and light weight. Thus, the market is apt to
employ the edge type backlight module because certain dimensions of
LCDs comprising the edge type module have those advantages.
However, a conventional light guide plate that forms uniform
V-shape grooves for guiding lights to a light output plane tends to
cause dark areas adjacent to the light input plane. The uniformity
of the overall brightness is, therefore, hard to control.
[0010] FIG. 1A is a conventional light guide plate that has uniform
V-shape grooves (i.e. the top angles of the V-shape grooves are
equivalent between the two opposing end portions of the light guide
plate, i.e. y.sub.1=y.sub.20). FIG. 1B is a schematic view
illustrating the dark areas adjacent to the light input portion in
view of FIG. 1A. An illumination device 1 (preferably a tube lamp)
emits lights into the light guide plate 2 through a first end
portion 24 of the light guide plate 2. Initially, the lights in the
light guide plate 2 usually travel in a total-reflections manner,
following Snell's Law. Soon after, the total-reflections gradually
diminish and the lights continuously travel in reflection and
refraction paths, wherein the refractive lights emit from a top
surface 22 as visible lights. Accordingly, the more frequently the
total reflections occur in the light guide plate 2, or the more
delay time between reflection and refraction paths, the less
frequently the refractive lights will emit from the effective
displaying area. It follows that the dark areas will increase and
the high performance visible region will decrease, which means that
the brightness of the overall display is not uniform. FIG. 1B shows
the dark areas occurring at the light input portions according to
the above-mentioned problems. These problems negatively affect the
products' performances in brightness and quality.
[0011] To diminish total reflections early on when the lights
travel in the light guide plate, a design that modifies this light
guide plate (as shown in FIG. 2) so that it has a tapered shape (as
shown in FIG. 3) is further created to initially introduce the
lights refracting out of the light guide plate, thereby reducing
the undesired dark areas adjacent to the illumination device 1.
[0012] Other similar designs have been developed as well. For
example, U.S. Pat. No. 5,485,354 discloses a light guide plate that
has a uniform thickness and a plurality of V-shape grooves formed
thereon with equivalent top angles. The V-shape grooves are formed
parallel to the light input plane (which is adjacent to the tube
lamp). The light guide plate, therefore, transmits the lights from
the tube lamp to the light output plane. Another example, U.S. Pat.
No. 6,576,887, discloses a gradually tapered light guide plate that
has a plurality of trapezoidal grooves formed parallel to the light
input plane (which is adjacent to a tube lamp). Likewise, the light
guide plate transmits the lights from the tube lamp to the output
plane.
[0013] However, too many total-reflections still exist in the light
paths that run within the light guide plate in the mentioned
conventional designs. These problems do not match the needs of a
high quality product that demands uniform brightness in the overall
display area.
[0014] Thus, a novel structure that further reduces the dark areas
on the edges, widens the viewing angles, and improves the overall
uniformity in brightness, is required in this field.
SUMMARY OF THE INVENTION
[0015] The primary objective of this invention is to provide a
light guide plate for use in a liquid crystal display (LCD). The
present invention is disclosed to diminish total-reflection areas
adjacent to the plane of light incidence by forming a plurality of
parallel V-shape grooves, which are formed on the bottom surface of
the light guide plate. The top angles gradually vary by increasing
from one end portion to the other opposing end portion.
[0016] Another objective of this invention is to provide a
backlight module for use in an LCD by using the novel light guide
plate as mentioned to diminish the dark areas on the edges of the
backlight module.
[0017] Yet a further objective of this invention is to provide an
LCD comprising the mentioned backlight module and a liquid crystal
panel disposed above the backlight module to make the brightness
uniform in the display area of the LCD.
[0018] According to the present invention, the V-shape grooves with
gradually varying top angles is adapted to efficiently reduce
total-reflections and introduce opportunities for earlier light
refraction after the lights enter the light guide plate. Lights
that initially travel in the light guide plate would immediately
have the chance to refract into visible lights and therefore
diminish dark areas adjacent to the plane of light incidence,
thereby enhancing the uniformity of the brightness of the whole
display.
[0019] The detailed technology and preferred embodiments
implemented for the subject invention are described in the
following paragraphs accompanying the appended drawings for people
skilled in this field to well appreciate the features of the
claimed invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1A is a schematic view illustrating a conventional
light guide plate with uniform V-shape grooves;
[0021] FIG. 1B is a schematic view illustrating the bright/dark
areas in view of FIG. 1A;
[0022] FIG. 2 is a schematic view illustrating frequent
total-reflective paths in a conventional light guide plate that has
a uniform thickness;
[0023] FIG. 3 is a schematic view illustrating rare
total-reflective paths in a conventional tapered light guide plate
that has a gradually converging thickness;
[0024] FIG. 4 is a schematic view illustrating the light guide
plate that has V-shape grooves with gradually increasing top angles
according to the present invention; and
[0025] FIG. 5 is a schematic end view illustrating V-shape grooves
at opposing ends of the light guide plate according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] FIG. 4 shows a preferred embodiment of the light guide plate
of the present invention. The tapered profile of the V-shape
grooves is gradually increasing top angles. More specifically, the
light guide plate 4 has a top surface 42, namely a light output
plane of the light guide plate 4, a bottom surface 43, a first end
portion 44 where the lights enter into the light guide plate 4, and
a second end portion 45 opposing to the first end portion 44. A
plurality of V-shape grooves formed on the bottom surface 43 of the
light guide plate 4 are substantially parallel and extends from the
first end portion 44 to the second end portion 45. Each V-shape
groove 41 has a top angle .gamma. which is varying, preferably,
gradually increasing, from the first end 44 (D.sub.1) to the second
end 45 (D.sub.20). The design of the V-shape groove 41 with the
gradually increasing top angle makes it possible for the lights to
refract early on from the first end 44 to and out from the top
surface 42 to provide visible lights for an LCD.
[0027] The thickness of the above-mentioned light guide plate 4 is
designated as d. Preferably, the thickness d gradually converges
from the first end portion 44 to the second end portion 45.
[0028] A localized region 5 could be enlarged and schematically
shown in FIG. 5. FIG. 5 is an end view illustrating the V-shape
groove 41 of the light guide plate 4 of the present invention. The
V-shape groove 41 is designed with a gradually increasing top
angle, from the first end portion 44, which is adjacent to an
illumination device, to the second end portion 45 (i.e. y.sub.1 to
y.sub.20).
[0029] The effects of the present invention could be realized after
experiments are performed in point of the mentioned structure. The
width measured from the first end portion 44 to the second end
portion 45 is divided into 20 segments (x=1 to 20), with the
gradually increasing top angles (y) following the optical
simulation equation:
y=-0.0146x.sup.2+1.9092x+107.69 (1)
[0030] The correspondences between x and y are shown in Table 1.
The first column "Distance 1.about.20" shows 20 segments (i.e.
D.sub.1.about.D.sub.20). The third column in Table 1 shows the top
angles y of the V-shape grooves 41 obtained from equation (1). The
actual top angles (y) of the V-shape grooves are shown in the
second column. The V-shape groove 41 has a top angle of 110.degree.
on the first end portion 44 (namely D.sub.1), that is to say,
y1=110'. The V-shape groove 41 also has a top angle of 140.degree.
on the second end portion 45 (namely D.sub.20), that is to say,
y.sub.20=140.degree.. A curve illustrating the angle variation is
also shown in Table 1.
[0031] According to the above mentioned angle variations of the
V-shape groove and the implementation of the optical simulation on
the visual angle of view of an LCD, levels of brightness and gains
in various angles of view are shown in Table 2. Angles between the
line of user's sight and normal of the light output plane are shown
in rows. For example, R90 represents the angles of view at
.+-.45.degree. in view of the normal on the plane of emergence.
Similarly, R05 represents the angles of view at .+-.2.5.degree. and
R02 represents the angles of view at .+-.1.degree. in view of the
normal on the light output plane. Three kinds of
grooves--Equivalent Angle (groove angle without variation), 2-stage
Angle (groove angle that varies at two stages only along the
width), and Complex Angle--are implemented and shown in columns in
Table 2. The Complex Angle, which is the groove angle that
frequently varies, is the one used according to the present
invention.
[0032] From the front, angles of view that are 5.degree.
(.+-.2.5.degree.) or 2.degree. (.+-.1.degree.) are most frequently
adopted by the user. In general, the brightness has better
performance as shown by the angles of views within 5.degree.. Table
2 shows the brightness that is measured as 1050.07 nit and 197.1
nit by the angles of views 5.degree. and 2.degree., respectively.
In comparison, measured brightness from equivalent grooves in the
conventional methods is 862.501 nit and 120.238 nit. Using complex
angles, the grooves in the present invention could increase
brightness by 21.75% in 5.degree. (.+-.2.5.degree.) and 63.92% in
2.degree. (.+-.1.degree.). Similar conclusions could be obtained
when the angle of view is 90.degree. (.+-.45.degree.).
[0033] Another embodiment of the present invention is a backlight
module for use with an LCD. Edge type backlight modules are
particularly valued in medium-size LCDs due to a smaller thickness
and fewer undesired heat problems. The backlight module of the
present invention comprises the mentioned light guide plate and an
illumination device (preferably a tube lamp). The illumination
device is disposed onto a lateral side of the light guide plate 4
(preferably on the outside of the mentioned first end portion 44)
for providing a projection light source from the first end portion
44 to the second end portion 45.
[0034] Still another embodiment of the present invention is a
liquid crystal display (LCD) comprising the mentioned backlight
module and a liquid crystal panel disposed above the backlight
module. The preferable panel according to the above embodiments
ranges from 15 inch to 19 inch.
[0035] With the top angle .gamma. of the V-shape groove that varies
from the first end portion 44 to the second end portion 45, a
desired reduction of the dark areas and increase in uniformity of
brightness may be achieved. In the case that the top angle .gamma.
of the V-shape groove gradually increases from the first end
portion 44 to the second end portion 45, either the height of the
triangle cross section of the groove will gradually decrease with
the increasing top angle under a constant hemline, or the hemline
of the triangle will gradually increase with the increasing top
angle under a constant height. Either option can still perform the
desired function in the above embodiment.
[0036] The above disclosure relates to the detailed technical
contents and inventive features thereof. People skilled in this
field may proceed with a variety of modifications and replacements
based on the disclosures and suggestions of the invention as
described without departing from the characteristics thereof.
Nevertheless, although such modifications and replacements are not
fully disclosed in the above descriptions, they have substantially
been covered in the following claims as appended.
* * * * *